AB1004 ACCURACY OF ICD10-AM M45 CODE FOR ANKYLOSING SPONDYLITIS IN A WESTERN AUSTRALIAN HOSPITAL COHORT
Authors: M. Isbel, K. Makin, J. Nossent
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Administrative linked health data (ALHD) facilitates epidemiological research of Ankylosing Spondylitis (AS) but best practice requires dataset validation<sup>[1]</sup>. While ICD10-code M45 is used to identify AS populations internationally it is also used to code "Rheumatoid arthritis of the spine"<sup>[2]</sup>. Neither background AS nor Rheumatoid arthritis (RA) is captured in ICD coding, unless actively flaring whilst the patient is admitted. <h3>Objectives</h3> To define the accuracy of ICD 10 Australian Modification (ICD10AM) code M45 in identifying AS patients in a tertiary hospital. <h3>Methods</h3> Retrospective audit of patients with an electronic hospital discharge code M45 between 2000 and 2015. Patient records were manually reviewed to confirm presence of AS based on following criteria a) radiological evidence of Grade IV sacroiliitis or "bamboo spine" b) fulfilment of classification criteria (1984 Modified NY, 1991 AMOR, 2002 ESSG and 2009 ASAS criteria)<sup>[3]</sup> c) letter from treating rheumatologist confirming AS d) Biological DMARD (bDMARD) prescription for treating confirmed AS. Cases that were not able to meet AS criteria and had a likely alternative diagnosis documented by their treating team had this detail noted, but not assessed against formal criteria. All patients were then evaluated to for presence of an RA code ever during that patient's lifetime. Codes used to define RA included by codes M08.0* M8.2*, M8.3*, M8.4*, M8.8*, M8.9*, M05.*, M06.* (ICD10) or 714 (ICD9). <h3>Results</h3> Of 155 cases reviewed, eighty-six (55.4%) met audit criteria for AS. Of the 69 cases not meeting audit criteria for AS, 35 (72%) had RA ICD codes applied during their lifetime and a further 15 had background RA recorded in their notes. Five cases met AS audit criteria and had RA code applied. Excluding patients ever tagged with an RA code reduced AS case finding by 6% and raised overall accuracy to 67.5%. If background RA is also excluded, accuracy is 78.9%. <h3>Conclusion</h3> Overall raw accuracy of the ICD10AM M45 code in identifying AS patients was low, with RA acting as a significant confounder. This bears significant implications for international ALHD research reliant on this code for case finding. Excluding those ever coded with RA significantly improved accuracy and is recommended for future research. Our data support the call for scrutiny of international variations of ICD taxonomy<sup>[4]</sup>. <h3>References</h3> [1]Bernatsky S, Lix L, O'Donnell S, Lacaille D. Consensus statements for the use of administrative health data in rheumatic disease research and surveillance. <i>Journal of rheumatology</i>. 2013;40(1):66-73. doi:10.3899/jrheum.120835 [2]ICD-10-CM Code for Ankylosing spondylitis M45. American Hospital Association. URL: Accessed 09/01/2023, 2023. https://www.aapc.com/codes/icd-10-codes/M45 [3]Sieper, J., Rudwaleit, M., Baraliakos, X., Brandt, J., Braun, J., Burgos-Vargas, R., Dougados, M., Hermann, K. G., Landewé, R., Maksymowych, W., &amp; van der Heijde, D. (2009). The Assessment of SpondyloArthritis international Society (ASAS) handbook: a guide to assess spondyloarthritis. <i>Annals of the rheumatic diseases</i>, <i>68 Suppl 2</i>, ii1–ii44. https://doi.org/10.1136/ard.2008.104018 [4]Jetté N, Quan H, Hemmelgarn B, Drosler S, Maass C, Moskal L, et al. The Development, Evolution, and Modifications of ICD-10: Challenges to the International Comparability of Morbidity Data. Medical Care. 2010;48(12):1105-10. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.